Mosques are visually richly furnished as a sign of respect to God?

Answer 1

More as a sign to self admiration of the builder.

As more distant of the truth you go, the more grandiose it gets.

The Tabernacle was the most significant and the only true God physical connection requirement, commanded to be built by God itself to Moses.

Later on, without any commandment it was replaced by the Temple in Jerusalem.

The Temple building was also the prominent promise of it's destruction.

So the Tabernacle was very simple, then the Temple was made of stone but yet simple, and then all nations built huge and crazy monuments and churches trying to overcome their emptiness and lie with grandiosity and humiliation of the observer.

Answer 2

Maybe. Grandiose buildings of all types are usually so furnished as a sign of respect for the person who put up the money to build them.

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It doesn't matter to be richly furnished or not. Mosques are usually clean and disciplined as a sign to God respect.